Dictionary
nep•tu•ni•um
Pronunciation: (nep-tOO'nē-um, -tyOO'-), [key]—
n. Chem., Physics.
a transuranic element produced in nuclear reactors by the neutron bombardment of U-238: decays rapidly to plutonium and then to U-235.
Symbol: Np;
at. no.: 93.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.